-SPECS-
In the ES5 spec, clauses 11.9.3.4-5 say:
If Type(x) is Number and Type(y) is String, return the result of the comparison x == ToNumber(y).
If Type(x) is String and Type(y) is Number, return the result of the comparison ToNumber(x) == y.
Clauses 11.9.3.6-7:
If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y.
If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).
Clauses 11.9.3.8-9:
If Type(x) is either String or Number and Type(y) is Object, return the result of the comparison x == ToPrimitive(y).
If Type(x) is Object and Type(y) is either String or Number, return the result of the comparison ToPrimitive(x) == y.
Note: In == comparison, coerce will happen until both become same type.
Observe: String and null is being compared
According to spec only null = undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: String and undefined is being compared
According to spec only null = undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: String and Boolean is being compared
Coercion: Boolean false is coerced to Number resulting 0
Read: "0" == 0
Observe: String and Number is being compared
Coercion: String "0" is coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: String and Number is being compared. Or more appropriately, NaN is never equal to itself or any other value
Coercion: String "0" is coerced to Number resulting 0
Read: 0 == NaN
Observe: Type matched or more appropriately, NaN is never equal to itself or any other value
Result: false
Observe: String and Number is being compared
Coercion: String "0" is coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: Two Strings are being compared
Coercion: No coercion happens
Observe: Type matched - value mismatched
Result: false
Observe: Boolean and null is being compared
According to spec only null == undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: Boolean and undefined is being compared
According to spec only null == undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: Boolean and Number is being compared. Or more appropriately, NaN is never equal to itself or any other value
Coercion: Boolean false is coerced to Number resulting 0
Read: 0 == NaN
Observe: Type matched or more appropriately, NaN is never equal to itself or any other value
Result: false
Observe: Boolean and Number is being compared
Coercion: Boolean false is coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: Boolean and String is being compared
Coercion: Boolean false coerced to Number resulting 0
Read: 0 == ""
Observe: Number and String is being compared
Coercion: String "" coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: Boolean and Array (Object) is being compared
Coercion 1: Boolean false is coerced to Number resulting 0
Coercion 2: Object is coerced using ToPremitive abstruct method resulting ""
Read: 0 == ""
Observe: Number and String is being compared
Coercion: String "" is coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: Boolean and Object is being compared
Coercion 1: Boolean false coerced to Number resulting 0
Coercion 2: Object is coerced using ToPremitive abstruct method resulting "[object Object]"
Read: 0 == "[object Object]"
Observe: Number and String is being compared
Coercion: String "[object Object]" is coerced to Number resulting NaN
Read: 0 == NaN
Observe: Type matched or more appropriately, NaN is never equal to itself or any other value
Result: false
Observe: String and null is being compared
According to spec only null == undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: String and undefined is being compared
According to spec only null == undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: String and Number is being compared. Or more appropriately, NaN is never equal to itself or any other value
Coercion: String "" is coerced to Number resulting 0
Read: 0 == NaN
Observe: Type matched or more appropriately, NaN is never equal to itself or any other value
Result: false
Observe: String and Number is being compared
Coercion: String "" is coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: String and Array (Object) is being compared
Coercion: Object is coerced using ToPremitive abstruct method resulting ""
Read: "" == ""
Observe: Type matched - value matched
Result: true
Observe: String and Object is being compared
Coercion: Object is coerced using ToPremitive abstruct method resulting "[object Object]"
Read: "" == "[object Object]"
Observe: Type matched - value mismatched
Result: false
Observe: Number and null is being compared
According to spec only null == undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: Number and undefined is being compared
According to spec only null == undefined or vise-versa
Coercion: No coercion happens
Result: false
Observe: Type matched or more appropriately, NaN is never equal to itself or any other value
Result: false
Observe: Number and Array (Object) is being compared
Coercion: Object is coerced using ToPremitive abstruct method resulting ""
Read: 0 == ""
Observe: Number and String is being compared
Coercion: String "" is coerced to Number resulting 0
Read: 0 == 0
Observe: Type matched - value matched
Result: true
Observe: Number and Object is being compared
Coercion: Object is coerced using ToPremitive abstruct method resulting "[object Object]"
Read: 0 == "[object Object]"
Observe: Number and String is being compared
Coercion: String "[object Object]" is coerced to Number resulting NaN
Read: 0 == NaN
Observe: Type matched or more appropriately, NaN is never equal to itself or any other
Result: false
Note: Underlying JavaScript engine may or may not follow exactly the same steps. I wanted to describe it as easy as hell.